This invention is generally directed to toner compositions, and developer compositions, and more specifically, the present invention is directed to toner compositions containing certain charge enhancing additives. The compositions of the present invention are useful in electrostatographic imaging systems, particularly those systems incorporating a Viton fuser roll.
Electrostatographic process, and more specifically the xerographic process is well known as documented in several prior art references. This process involves the development of an electrostatic latent image by applying toner particles to the image to be developed using, for example, cascade development, magnetic brush development, touchdown development, and the like. The toner particles applied can be charged negatively or positively, depending upon the charge deposited on the photoreceptor surface. Thus, for example, if it is desired to develop a negatively charged imaging surface, the toner particles are positively charged usually by incorporating therein certain charge enhancing additives.
Numerous types of charge enhancing additives are known in the prior art, including those which impart a positive charge to the toner composition. For example, there is disclosed in U.S. Pat. No. 3,893,935 the use of certain quaternary ammonium compounds as charge control agents for electrostatic toner compositions. According to the disclosure of this patent, certain quaternary ammonium compounds when incorporated into toner materials were found to provide a toner composition which exhibited relatively high uniform and stable net toner charge when mixed with a suitable carrier particle. A similar teaching is contained in U.S. Pat. No. 4,079,014 with the exception that a different charge control agent is used, namely, a diazo type material. Additionally, there is described in U.S. Pat. No. 4,298,672 toner compositions containing as positive charge enhancing additives alkyl pyridinium materials, including cetyl pyridinium chloride.
Additionally, there is disclosed in U.S. Pat. No. 4,338,390, charge control additives compatible with Viton fuser systems, which additives are comprised of organic sulfate or sulfonate materials, including stearyl dimethyl phenethyl ammonium para-toluene sulfonate, and the like.
While the charge enhancing additives described in the prior art are suitable for their intended purposes, that is for imparting a positive charge for example, to the toner resin, many of these additives interact with certain fuser rolls incorporated into the electrostatographic imaging system. For example, it is known that certain prior art charge enhancing additives adversely affect Viton fuser rolls, causing a deterioration in the quality of images developed in electrostatographic copying systems containing such rolls. Thus, for example, Viton fuser rolls discolor and turn black, as well as develop multiple surface cracks when developer compositions containing many of the prior art charge control additive compounds contact the Viton fuser roll.
An example of one type of Viton fuser roll used in electrographic copying machines, particularly xerographic copying machines, is comprised of a soft roll fabricated from lead oxide and duPont Viton E-430 resin (a vinylidene fluoride, hexafluoropropylene copolymer). Approximately 15 parts of lead oxide and 100 parts of the Viton E-430 are blended together and cured on a roll at elevated temperatures. Apparently the function of the lead oxide is to generate unsaturation by dehydrofluorination for crosslinking, and to provide release mechanisms for the toner. Excellent image quality has been obtained with the use of Viton fuser rolls, however, in some instances there is a toner fuser compatibility problem when charge control agents are contained in the toner mixture. For example, it is believed that certain quaternary ammonium charge control additives, and alkyl pyridinium compounds react with the Viton fuser roll. Thus, an alkyl pyridinium chloride, such as cetyl pyridinium chloride when part of the toner mixture appears to attack the fuser roll, resulting in a highly unsaturated compound which polymerizes and condenses with the unsaturated Viton. As a result the Viton fuser turns black, and develops multiple surface cracks, thereby resulting in image quality deterioration.
There thus continues to be a need for improved charge enhancing additives for incorporation into toner compositions, and developer compositions. Additionally, there continues to be a need for charge enhancing additives which impart a positive charge to the toner resin particles. Also, there is a need for toner compositions and developer compositions which contain charge enhancing additives that do not adversely affect fuser rolls, and in particular, Viton fuser rolls selected for use in electrostatographic imaging systems. Additionally, there is a need for charge enhancing additives which can be prepared by a simple, direct, economical process, thereby decreasing the cost of the toner compositions involved. Furthermore, there continues to be a need for toner compositions which will rapidly charge new uncharged toner particles which are added to a positively charged toner of the same composition.